A ratchet device typically comprises a mandrel device with a grooved area and a locking device comprising locking grooves configured to be engaged with the grooved area of the mandrel device. Axial movement between the mandrel device and the locking device is allowed in a first direction when the locking device is engaged with the mandrel device while movement between the mandrel device and the locking device is prevented in a second direction opposite of the first direction. Hence, a ratchet device may be considered as a locking mechanism for preventing relative movement between two parts in one direction only.
Such ratchet devices are commonly used in tools and/or other type of equipment for use in oil and/or gas wells, such as packers, plugs, straddles etc., where the ratchet device typically is used to allow the tool to be brought from a first state to a second state (for example from a run state to a set state) while preventing the tool going from the second state and back to the first state.